Method of producing sintered electrodes



June 13, H967 H. EBHARDT 35325 2331 METHOD OF PRODUCING SINTEREDELECTRODES Filed July 2, 1965 2 Sheets-Sheet 1 How/s! Elalwmoif INVENTORJune 396? H. EBHARD"? 3325 21 METHOD OF PRODUCING SINTERED ELECTRODESFiled July 2, 1965 2 Sheets-Sheet 2 WGQM H 151 Einkcveo -f INVENTOR.

United States Patent 3,325,281 METHQD OF PRODUCHNG SlNTERED ELECTRGDESHorst Ebhardt, Graz Andritz, Australia, assignor to Elin- UnionAlktiengesellschaft tiir elektrische Industrie,

Vienna, Austria Filed July 2, 1965, Ser. No. 469,165 Claims priority,application Austria, July 8, 1964, A 5,864/64 6 Claims. (Cl. 75-206)ABSTRACT OF THE DISCLUSURE The invention relates to a method ofproducing sintered electrodes, particularly for low pressure vapordischarge tubes which are activated with peroxide sand/or oxides of thealkaline-earth metals, if desired with iron, tantalum, tungsten,zirconium, molybdenum, or the like, by applying the mixture under apressure ranging from 1000 to 2000 kg./cm. into the body of saidelectrode and heating the activated mass until a splattering of aninsubstantial portion of the activation mass occurs.

Background of the invention Field of the invention: The inventionrelates to sintered electrodes for electrical glow discharge lamps inwhich a metal powder is intimately mixed with an activating substanceconsisting of a peroxide or oxide of an alkaline earth metal andsubsequently heated.

Description of prior art Prior known low pressure vapor discharge tubesas a rule have electrodes which possess an incandescent coil butalthough these occupy but little space they are subject, among othernumerous disadvantages, to heavy wear. The useful life of these knownlow pressure vapor discharge tubes is relatively short, being in theneighborhood of at the utmost about 5,000 burning hours.

It is moreover already known to reduce the cathode drop by highlycharging a glow discharge cathode, so prepared as to lower the cathodedrop, to values below 50 volts, the preparation with a view to loweringthe cathode drop being effected by spraying on a paste of carbonates ofalkaline earths and by activation.

Vapor discharge tubes are also known in which the electrodes areprovided in the shape of cup electrodes which have an activation layerwhose emitting substances contain oxides of the metals calcium,strontium or barrum.

Generally speaking, the prior known electrodes of the type describedabove were made by the method in which the activation composition, asthe part emitting electrons, was pressed in the form of a compact body,somewhat in the form of a pill, under high pressure into or on to a moreor less cylindrical, annular or hemispherical elec trode body.

It has been found that the electrodes produced by the known methods didnot give the results expected of them either as regards their usefullife or as regards the reduction of ignition and operating voltages.

It is the object of the invention to provide a method by which sinteredelectrodes can be manufactured which have the longest possible usefullife, permit the production of vapor discharge tubes of great length inspite of the use of low voltage, and possess the least possible heatdissipation despite high loadability and hence high light intensity.

Summary 0] the invention According to the invention, a powder of iron,tantalum, tungsten, zirconium, molybdenum, or the like, is intimatelymixed by mechanical means with peroxides and/ or oxides of thealkaline-earth metals and the mixture inserted into an electrode body,specifically a metal cup, in such a manner that the activation mass isin conductive connection with the electrode wire, whereupon theactivation mass is forced under pressure into the electrode body and isthereafter heated, for example with the aid of a high frequencygenerator, until a Slight explosion occurs; the explosive pressure is soguided in one direction that only an inconsiderable part of theactivation mass spurts out of the electrode body and the visible part ofthe activation mass exhibits after the sintering, a porous and roughsurface.

It is evident that the activation mass shows at the moment of explosiona tendency to escape in the direction of least resistance. Owing to thefact that the activation mass spreads out in this direction, the visiblepart of said mass exhibits a rough and porous surface, which inconsequence of its consistency and character substantially facilitatesthe formation of a discharge glow point, whereby the cathode drop isnotably reduced.

The original mixture advantageously consists, in a manner known per se,either of iron, tungsten, zirconium, molybdenum or the like in powderform, which is simply but very thoroughly mixed with barium oxide, orelse the mixture is made up of zirconium, tantalum or tungsten andperoxide or of barium oxide and of carbonyl iron and tantalum powder.

The mixture advantageously consists of two parts of oxides or peroxidesof alkaline-earth metals, particularly barium peroxide or oxide, and onepart of metal powder, particularly iron powder, with an allowance ofEspecially good results have been found when the pulverulent activationmass is pressed into the electrode body under a pressure of about 1,000to 2,000 kg./cm. and the pressed-in mass is heated to produce theexplosion.

A further advantageous development of the invention consists in that theelectrodes are fused into a glass body, particularly a glass cylinder,and subsequently tempered at a maximum temperature of 450 C.

The electrodes produced by the method of the invention exhibit anextremely high endurance and can be loaded with current intensities ofto 180 milliamperes. The endurance is moreover unaffected by switchingfrequency.

The accompanying drawing illustrates a few conventional forms ofelectrodes or low pressure vapor discharge tubes, which are particularlywell suited for carrying out the method according to the presentinvention.

Brief description of drawing FIGURE 1 shows schematically a low pressurevapor discharge tube with cup electrodes made in accordance with theinvention, with part of the tube broken away,

FIGURE 2 shows in a similar manner a low pressure vapor discharge tubewith attachments for receiving the electrodes,

FIGURES 3 to 6 show different cup-shaped forms of electrodes,

FIGURE 7 shows an especially advantageous annular form of electrode insection along the line VIIVII in FIGURE 8, and

FIGURE 8 shows the same form of electrode in plan view, while FIGURES 9to 13 show further forms of electrodes.

Description of the preferred embodiments In the example illustrated inFIGURE 1, representing a low pressure vapor discharge tube filled, forexample, with mercury vapor in a known manner and having on the inside acoating of luminous substance (not shown), the electrodes 2 are arrangedin the tube 1 coaxially therewith. The electrodes 2 are in this case cupelectrodes constructed in the form of cylindrical pots provided withbottoms in which the activation layer as the part emitting electrons isarranged in the form of a compact body 3'. The electrodes 2 are providedwith connection pins or wires 4 leading from the inside of the tube tothe outside. The layer of luminous substance can, in this case extendpractically from one end of the tube 1 to the other, so that a tube ofthis kind, in which the electrodes 2 are arranged at a short distancefrom its ends is luminous throughout its whole length during operation.

If it is desired to produce long luminous bands Without any dark gaps, anumber of tubes as in FIGURE 1 can be arranged end to end in series.However, a more suitable solution is represented by the low pressureluminous tube shown in FIGURE 2, in which at the ends of the tube 1, atright-angles to the longitudinal extension thereof, short tubularattachments are arranged in which the electrodes 2 are housed. In thisform of construction, electrodes 2 are provided such as are shown indetail in FIGURES 7 and 8. The end faces of the tube 1 are made fiat inorder that, with the layer of luminous substance extending throughoutthe'entire length of the tube, there is practically no break in thecontinuity of the luminous band when a number of the tubes are placedend to end in a row.

FIGURE 3 shows a cylindrical cup electrode which in itself may have anydesired shape of cross-section. In this example the mixture ofcomposition 3 emitting electrons is disposed at the bottom of a metalbeaker 6 provided with a lead-in 4. It is clear that in the carrying outof the method according to the invention with the form of cup electrode6 shown in the figure the explosive pressure will be directed towardsthe open end of the cup and only an inconsiderable portion of theactivation mass can spurt out of the cup.

The shape of the cup itself can vary as desired. Thus FIGURE 4illustrates a funnel-shaped cup, the mass 3 emitting electrons beingaccommodated in the tip of the funnel-shaped cup, which is likewiseequipped With a lead-in 4. This cup, too, can be made circular,rectangular, or the like. FIGURE 5 shows a cup shaped like a hollowball, and FIGURE 6 one shaped like a cap.

An especially useful electrode is illustrated in FIG- URES 7 and 8. Herethe electron-emitting mass 3 is laced between two cylinders 7 and 8which are arranged one within the other and the diameters of whichdiffer only slightly, thus leaving a comparatively narrow space for theelectron-emitting mass 3. For feeding current by means of the pin orwire 4, and as a means of holding the electrode, support 9 issuflicient, which may have any desired shape. The ring formed by theelectron-emitting mass 3 can also have a polygonal shape, for example berectangular. FIGURE 9 shows an annular electrode, similar to theelectrode according to FIGURES 7 and 8 but having in this case a support9 of, for example, insulatlating material and current lead-in 10 in theform of a wire.

FIGURES 10 and 11 illustrate an example of an electrode which is made upof a few walls 11 extending in parallel which constitute a plurality ofchambers filled with the mass 3 emitting electrons, FIGURE 10 being aplan view and FIGURE 11 a side view of this embodiment.

Another electrode suitable for the method of the invention is seen inFIGURES 12 and 13, FIGURE 12 being a section along the line XIII-XIII inFIGURE 13. In this example the cup, provided with the wall 7 andcontaining the electron-emitting mass 3 in its bottom, is surrounded bya wall 8. Instead of the cup with the wall 7, a disc, a bar, a ring,etc., can be used to carry the electron-emitting mass 3. Moreover,instead of the circular shape, any other geometrical figure can bechosen.

' What I claim is:

1. In a process for making sintered electrodes for electrical glowdischarge lamps, in which a metal powder is mechanically intimatelymixed with an oxidizing substance selected from the group consisting ofperoxides and oxides of alkaline earth metals and the mixture applied asan activation mass to the body of the electrode to be sintered underpressure and subsequently heated, the improvement that the mixture isapplied to the electrode body under a pressure ranging from 1000 to 2000'kg./cm. the mixture consisting of 2 parts of oxidizing substance, 1part of metal powder and the heating continued for a time sufficient tospatter the activation mass, the pressure causing said spattering beingdirected in such a manner, by covering the activation mass, that only aninsubstantial portion of said mass will be sprayed off from theelectrode body, while the bulk of said mass remains applied to saidbody.

2. The process according to claim 1, wherein the oxidizing substanceconsists of barium oxide or peroxide and the metal powder of iron withan allowance of 20%.

3. The process according to claim 1, wherein the metal powder is amember selected from the group consisting of iron, tungsten, zirconiumand molybdenum power, and the oxidizing substance is barium oxide.

4. The process according to claim 1, wherein the metal powder consistsof zirconium, tantalum or tungsten and the oxidizing substance is aperoxide of alkaline earth metal.

5. The process according to claim 1, wherein the metal powder is amixture of carbonyl-iron and tantalum powder and the oxidizing substanceis barium oxide.

6. The process according to claim 1, wherein the electrodes after fusingthem into lamp bulbs, are tempered at a maximum temperature of 450 C.

References Cited UNITED STATES PATENTS 2,117,636 5/1938 Tjoflat 29l82.52,175,345 10/1939 Gaidies et al. 313346X 2,753,615 7/1956 Claude et al.2925.17 2,953,443 9/1960 Lloyd 149-37 BENJAMIN R. PADGETT, PrimaryExaminer.

L. DEWAYNE RUTLEDGE, Examiner.

R. L. GRUDZIECKI, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No,3,325,281 June 13, 1967 Horst Ebhardt It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

In the heading to the printed specification, line 4, for "Australia"read Austria column 2, line 43, for "150 to 180" read 150 to 800 Signedand sealed this 26th day of November 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, J r.

Commissioner of Patents Attesting Officer

1. IN A PROCESS FOR MAKING SINTERED ELECTRODES FOR ELECTRICAL GLOWDISCHARGE LAMPS, IN WHICH A METAL POWDER IS MECHANICALLY INTIMATELYMIXED WITH AN OXIDIZING SUBSTANCE SELECTED FROM THE GROUP CONSISTING OFPEROXIDES AND OXIDES OF ALKALINE EARTH METALS AND THE MIXTURE APPLIED ASAN ACTIVATION MASS TO THE BODY OF THE ELECTRODE TO BE SINTERED UNDERPRESSURE AND SUBSEQUENTLY HEATED, THE IMPROVEMENT THAT THE MIXTURE ISAPPLIED TO THE ELECTRODE BODY UNDER A PRESSURE RANGING FROM 1000 TO 2000KG./CM.**2, THE MIXTURE CONSISTING OF 2 PARTS OF OXIDIZING SUBSTANCE, 1PART OF METAL POWDER AND THE HEATING CONTINUED FOR A TIME SUFFICIENT TOSPATTER THE ACTIVATION MASS, THE PRESSURE CAUSING SAID SPATTERING BEINGDIRECTED IN SUCH A MANNER, BY COVERING THE ACTIVATION MASS, THAT ONLY ANINSUBSTANTIAL PORTION OF SAID MASS WILL BE SPRAYED OFF FROM THEELECTRODE BODY, WHILE THE BULK OF SAID MASS REMAINS APPLIED TO SAIDBODY.